Vacuum blood collection tubes for plasma contain heparin salts which are applied to the internal walls of the tube (heparin content: 12-30 IU/mL of blood). As an anticoagulant, heparin activates antithrombins and blocks the clotting cascade in the blood sample. Tubes with a separation gel are used to ensure a stable barrier between the formed elements and blood plasma after centrifugation. Acti-Fine ® tubes for collecting plasma are used in biochemical tests and express testing so that there is no need to wait up to 30 minutes for clotting.